A press apparatus served for a drawing process of a steel plate is conventionally classified broadly into a hydraulic press apparatus using a hydraulic pressure, and a mechanical press apparatus on the basis of a mechanical drive force by a pressure generating mechanism, however, they are classified into a single action type and a double action type on the basis of a motion type of a slide. Further, the mechanical press apparatus is classified into a crank press, a knuckle press, a link press, a friction press and the like on the basis of a drive mechanism of the slide.
Among the structures mentioned above, the double action type mechanical press apparatus is structured such that an outer slide and an inner slide provided in an inner side of the outer slide are independently moved upward and downward by a drive portion, the outer slide moves downward prior to the inner slide at a time of pressing a blank, an outer die attached thereto presses a peripheral edge portion of the blank, and a draw molding or the like of the blank is next performed by the downward movement of the inner slide (refer, for example, to Japanese Unexamined Patent Publication No. 8-103827).
As mentioned above, in the conventional mechanical press apparatus on the basis of the double action type, since the outer slide presses the blank prior to the inner slide, there is an advantage that a deep drawing of the blank can be stably and well achieved in comparison with the single action type.
However, the conventional mechanical press apparatus on the basis of the double action type requires two molds for each of upper and lower molds, such as an outer die and an inner die (a punch) serving as the upper mold, and a blank holder corresponding to the outer die and a cavity corresponding to the inner die serving as the lower mold, and a structure of the drive portion is complex in comparison with the single action type. Accordingly, there is a disadvantage that a high cost is required.
Further, the conventional mechanical press apparatus on the basis of the double action type is generally placed at the head of a tandem line in order to suit for a deep drawing, and the single action type generally forms the blank in a convex shape. On the contrary, since the double action type performs a concave shape, it is necessary to reverse upper and lower surfaces of the blank by equipping a turn-over device between the double action type and the single action type. Accordingly, there is a problem that a productivity of the press molded product is deteriorated.
In particular, in the conventional mechanical press apparatus on the basis of the double action type, since a drive force distributed to the outer slide and the inner slide is determined by the structure of the drive portion, a pressing capacity of the outer slide and the inner slide can not be changed in correspondence to a material and a thickness of the blank. Further, if the inner die is enlarged, the inner die is interfered with the outer die. Accordingly, a product pressed thereby is limited to a magnitude of an inner side of the outer slide.
Accordingly, in recent years, the single action type press apparatus is mainly employed for the purpose of corresponding to an increase in size of the press molded product such as a motor vehicle body or the like and improving a productivity, and the mechanical press apparatus which is of the double action type, has a small pressing capacity and is hard to be modified for increasing the capacity is not used very much, and is under an actual condition of being anxious about a countermeasure thereof.
The present invention is made by taking the circumstances mentioned above into consideration, and an object of the present invention is to make it possible to preferably press mold a large-sized blank at a high pressure by employing a single action use aspect while being of a double action type.